This invention relates to a roll construction whereby pressurized fluid is introduced near the edges thereof to vary the effective rigidity while maintaining a constant rigidity in the crown area. More particularly, in order to obtain a more uniform thickness across the width of a rolled product, the rolling pressure is particularly controlled near the ends of the product.
In conventional multiple rolling mills, it is customary to effect control of the thickness and shape of a product being rolled by performing one or a combination of several well-known methods, such as correcting the deflection of the work rolls or the back-up rolls by providing counter roll bending forces between these rolls, and/or providing a crown on the work rolls in addition to providing quick acting screw down device.
Normally when using these conventional methods, the profile of the product in a transverse direction consists of a crown in the center tapering off at both ends which is referred to in the industry as "edge drop" where the thickness near the ends of the product is less than that at its center.
This "edge drop" condition or over rolling essentially occurs for at least two reasons: one reason being that the effective rolling load near the edges of the product is greater than the rolling load in the center of the product thereby causing the rolls of the mill to deliver a greater force to the portions of the roll contacting the edges of the strip; and the other reason being there is more lateral spreading and therefore less resistance from the material near the ends of the product upon the application of the rolling forces of the rolls during the rolling process.
Several methods for reducing or eliminating the degree of this "edge drop" are known in the industry; for instance, tapering the ends of the work rolls; or shortening the back-up rolls when used in conjunction with work rolls; or axially shifting the work rolls or an intermediate roll especially in a five or six high roll arrangement.
There are several drawbacks to these above methods and/or their structural features for carrying out the respective methods. One drawback is that when tapering the roll ends or for shortening the work rolls, only a limited range of product width can be rolled. A drawback inherent in the axial shifting of one of the rolls is that the shifting operation normally can be done only in between the sequential rolling of products and not while the product is actually being rolled.